Slavery is a system used to control people against their will, usually through violence or other forms of coercion, and in historical terms slavery is often associated with chattel slavery, an economic system in which laborers are considered the property of their masters.
This is a general category for sites on the history of slavery, which is almost always by definition "social history." Sites dealing with the social history of slavery can be submitted from any time period, culture, or location. ODP has several related categories, like Society: History: By Time Period: Eighteenth Century: Slavery, Society: History: By Region: Africa: Slavery, Society: Religion and Spirituality: Christianity: Denominations: Catholicism: History: By Topic: Slavery; sites for any of these categories can be submitted here or to those categories, which are cross-listed here. Sites dealing with ongoing, contemporary forms of slavery should not go here but be submitted to Society: Issues: Labor: Slavery.
Websites on historical aspects of slavery in North America, particularly (but not exclusively) in the United States and the Caribbean region.